CARBONIFEROUS PERIOD. 157 



Subclass DKECA. 

 Order RHIPHIDOGLOSSA. 



StHBORDER DIORANOBRANCeiA. 



Family BELLER0PH0NTIDJ3. 



Genus BELLEROPHON Montfort, 1808. 



Bellerophon crassus Meek and Worthen. 



Plate XII, fig. 1 a. 



Bellerophon crassus Meek and Worthen, 1860, Proc. Acad. Nat. Sci. Phila., 458. 

 Bellerophon crassus Meek and Worthen, 1860, Geol. Surv. Illinois, ii, 3S5. 



Shell large, massive, subglobose ; volutions gradually expanding lat- 

 erally, broadly rounded upon the back, more abruptly rounded at the sides 

 and into the umbilici, which are rather small ; outline of aperture reniform, 

 its transverse diameter greatest ; jiostero-lateratportions of the lip thickened 

 and spread outward and backward over the inner volutions and also partly 

 over the umbilici ; antero-lateral portions of the lip thinner, their margins 

 slightly convex on each side of the mesial notch ; mesial band narrow, 

 more or less distinct ; mesial notch not deep. 



Surface marked by distinct lines of growth, a part of which assume 

 the character ox somewhat irregular transverse wrinkles. 



The collections contain only a single specimen of this well-marked 

 species, which, although it measures thirty-eight millimeters across the 

 aperture, is " one-quarter smaller than one of the type-specimens used by 

 Meek and Worthen in their description of the species. 



The types were obtained from the Lower Coal-Measures of Illinois, 

 and the species is also known to occur in the Upper Coal-Measures of Iowa 

 and Missouri. So far as I am aware, it has not been found in the Lower 

 Coal-Measures of the two last-named States. 



Position and locality. — Strata of the Carboniferous period; Camp Cot- 

 tonwood, near Spring Mountain, Nevada. 



